The signs and symptoms of lichen planus vary depending on the areas affected. Typical signs and symptoms are:

• Purplish, flat bumps, most often on the inner forearm, wrist or ankle, and sometimes the genitals
• Itching
• Blisters that break to form scabs or crusts
• Lacy white patches in the mouth or on the lips or tongue
• Painful sores in the mouth or vagina
• Hair loss
• Change in scalp color
• Nail damage or loss

Lichen planus occurs when your immune system attacks cells of the skin or mucous membranes. It's not clear why this abnormal immune response happens. The condition isn't contagious.

Lichen planus can be triggered by:

• Hepatitis C infection
• Flu vaccine
• Certain pigments, chemicals and metals
• Pain relievers, such as ibuprofen (Advil, Motrin IB, others) and naproxen (Aleve, others)
• Certain medications for heart disease, high blood pressure or arthritis

Anyone can develop lichen planus. But the condition most often affects middle-aged adults. Oral lichen planus most often affects middle-aged women.

Lichen planus can be difficult to manage on the vulva and in the vagina, causing severe pain and sometimes leaving scars. Sexual dysfunction can become a long-term complication. Oral sores may affect your ability to eat. The affected skin might stay slightly darker even after the rash clears up, especially in dark-skinned people.

Oral lichen planus increases the risk of oral cancer. Left untreated, lichen planus of the ear canal may lead to hearing loss.